I. Field of the Invention
The present invention relates to the field of semiconductor on insulator technology. More particularly, the present invention relates to semiconductor devices having an insulator layer with improved thermal conductivity, made from a polymer precursor to ceramic, and a method of making the same.
II. Description of the Related Art
The microelectronics industry, such as the semiconductor device industry, is driven by market demands to increase continually the speed, bandwidth, and performance of its devices. Generally, it is also advantageous to reduce the size of the devices while maintaining or improving performance and speed. Driven by and reflecting this demand, the clock speed, for example, of microprocessors is increasing every year as reflected by the aphorism commonly known as Moore""s Law. One of the critical problems in the continued advancement of microelectronics is the capacitance of the transistors and other design components in the chip. Semiconductor on insulator (SOI), such as silicon on insulator, technology offers the advantage over conventional bulk semiconductor technology of reducing the area junction capacitance of the device. This decrease in capacitance leads to higher possible speeds for a given device. A typical estimate is that the silicon on insulator technology using SiO2 as the insulator offers a performance improvement between 20 and 35% over bulk silicon (SOI technology for the GHz era, IBM research journal, Shahadi). Devices with lower junction capacitance can also require less power. Higher speed is required to continue advancing the technological capabilities of electronics; lower power consumption is a critical need for portable electronics.
Turning to the prior art of silicon on insulator, one well-known method is to bond two silicon wafers, one or both having an oxide layer, together using a high-temperature fusion process. Using chemo-mechanical lapping or a slicing technique, one of the silicon wafers is then nearly lapped or sliced completely away to form a silicon on oxide layer. This method produces an entire wafer of silicon on insulator.
Another method is SIMOX (Separation by Implanted Oxygen) technology. In this case, the surface of the wafer is implanted with oxygen to a fixed depth and then the wafer is annealed in order to bury the oxygen. Recent advancements in control of the SIMOX step have led to this approach being successfully commercialized. This method produces an entire wafer of silicon on insulator.
Other methods, such as U.S. Pat. No. 5,185,286 to Eguchi, U.S. Pat. No. 5,321,298 to Moslehi, and U.S. Pat. No. 6,239,469 to Bolam, allow for forming regions of silicon on insulator.
The disadvantage of each of these approaches is that the insulator is either an oxide or a nitride. Typically, these layers are also good thermal insulators. Generally, it is well-known that microelectronic components work better and more reliably at lower temperature, therefore an insulating layer that also conducts heat well would be a benefit. The present invention is directed toward a method of fabricating the insulator layer from a ceramic material with high thermal conductivity and high electrical resistivity.
Polymer precursors to ceramic are described generally in U.S. Pat. No. 5,516,884 to Bianconi. Bianconi discloses a broad range of polymer precursors to ceramic, method of manufacturing these substances and suggests some possible uses. The present invention is directed towards the use of specific, improved polymer precursors to ceramic as the insulator layer of a silicon-on-insulator semiconductor substrate. Specifically, Bianconi implies that it is desirable to minimize or eliminate the halogens from the final compound during formation of the PPTC, while the present inventors have discovered that the presence of such halogens in general, and chlorine in particular, is advantageous when the PPTC is used as the insulator layer of a silicon on insulator substrate.
Accordingly, the present invention solves the above needs through the use of a polymer precursor to ceramic. Unlike the conventional insulating material for silicon on insulator devices and wafers, a polymer precursor to ceramic can be easily applied and converted to ceramic to serve as the insulating layer in a semiconductor on insulator substrate, providing the desired properties of high thermal conductivity and low area junction capacitance.
In a preferred embodiment, the polymer precursors to ceramic have the chemical formula [CR]n, more fully defined below. Preferred embodiments may further have the formula (CH)n(X)m, described below. These polymer precursors to ceramic, when converted to ceramic, offer a layer which is an electrical insulator while having increased thermal conductivity.
The polymer is applied to the device using a variety of methods appropriate for the application of fluids to a surface, such as dispensing on a spinning substrate akin to a typical photoresist dispensation. Other suitable methods include spraying, dipping, or wiping. After conversion to ceramic, the polymer can be processed to provide exceptional surface smoothness, with or without subsequent polishing operations.
When applied to the method for making semiconductor on insulator devices, such as silicon on insulator devices, the electrical resistivity of the ceramic beneath the device decreases the area junction capacitance, thus allowing for increased speeds over the bulk semiconductor, similar to the same method using SiO2, and allows for increased thermal transfer through the ceramic layer. By helping to wick away the heat generated by the device, the ceramic layer allows for higher power levels or for cooler operation. Cooler operation will extend the life of the device and reduce temperature related variations in its performance. Higher power levels allow devices to switch more power or to run faster or both.
It is therefore an object of the invention is to provide a method for forming a semiconductor on insulator structure across an entire wafer using a polymer precursor to a ceramic, such as SiC or Diamond, as the insulator layer.
Another object of the invention is to provide a method for forming a semiconductor on insulator structure across an entire wafer using a polymer precursor to a ceramic, such as SiC or Diamond, as the insulator layer that provides a smooth surface for the subsequent growth of the semiconductor layer.
A further object of the invention is to provide a method for forming a semiconductor on insulator structure across an entire wafer using a polymer precursor to ceramic, such as SiC or Diamond, as the insulator layer that provides a more thermally conductive layer to improve heat conduction away from the device.
Another object of the invention is to provide a method for forming a semiconductor on insulator structure across an entire wafer using a polymer precursor to a ceramic that provides a lower capacitance between the device and the substrate.
A further object of the invention is to provide a method for forming a semiconductor on insulator structure across an entire wafer using a polymer precursor to an amorphous material, such as amorphous diamond-like carbon, as the insulator layer to prevent lattice mismatch between the insulator and the semiconductor layer.
Another object of the invention is to provide a method for forming a semiconductor on insulator structure on a region of a wafer.
A further object of the invention is to provide a method for forming a semiconductor on insulator structure on a region of a wafer using a polymer precursor to a ceramic, such as SIC or Diamond, as the insulator layer that provides a smooth surface for the subsequent growth of the semiconductor layer.
Another object of the invention is to provide a method for forming a semiconductor on insulator structure on a region of a wafer using a polymer precursor to ceramic, such as SiC or Diamond, as the insulator layer that provides a more thermally conductive layer to improve heat conduction away from the device.
A further object of the invention is to provide a method for forming a semiconductor on insulator structure on a region of a wafer using a polymer precursor to a ceramic that provides a lower capacitance between the device and the substrate.
Another object of the invention is to provide a method for forming a semiconductor on insulator structure on a region of a wafer using a polymer precursor to an amorphous material, such as amorphous diamond-like carbon, as the insulator layer to prevent lattice mismatch between the insulator and the semiconductor layer.